The present invention relates to a process for preparing di- and trialkylsilanes having bully allyl radicals by hydrosilylation of alkenes with hydrogen-containing silanes in the presence of a transition metal catalyst and an activator.
Dialkyldialkoxysilanes having bulky alkyl radicals on the silicon are now sought by virtually all relatively large polypropylene manufacturers for their Ziegler catalysts of the latest generation. Particularly sought after are silanes having short-chain branched alkyl or cycloalkyl groups. Until recently, these silanes were industrially produced exclusively from chlorosilanes or alkoxysilanes by the expensive organometallic route, i.e., using large amounts of metals such as sodium or magnesium and also solvents, with corresponding large amounts of metal-containing by-products having to be disposed of.
Alkyl- or dialkylsilanes in which at least one of the alkyl radicals has at least 2 carbon atoms and which contain chlorine atoms or alkoxy radicals in addition to hydrogen bonded directly to silicon add, in the presence of noble metal catalysts, in a satisfactory manner only to linear alkenes having a terminal double bond, so-called .alpha.-olefins. Thus, the hydrosilylation of branched or cyclic alkenes having at least 4 carbon atoms with silanes such as dichlorosilane having 2 hydrogen atoms bonded directly to silicon leads only to a monoalkylchlorosilane, even if the alkene is present in excess.
EP-A-602 922 describes a process for reacting both hydrogen atoms of chlorine- or alkoxy-containing silanes having 2 hydrogen atoms bonded directly to silicon with cyclic alkenes having at least 4 carbon atoms in the presence of oxygen. However, the passing in of oxygen as described is complicated and dangerous since the hydrogen-containing silanes, which are readily combustible can form ignitable mixtures with oxygen and the further reaction components.